Re: [PATCH v4 net-next 3/6] drivers: net: dsa: add locked fdb entry flag to drivers

[netdev]

On 2022-08-22 07:40, Ido Schimmel wrote:
> On Sun, Aug 21, 2022 at 03:43:04PM +0200, netdev@xxxxxxxxxxxxxxxxxxxx 
> wrote:
>
> I personally think that the mv88e6xxx semantics are very weird (e.g., 
> no
> roaming, traffic blackhole) and I don't want them to determine how the
> feature works in the pure software bridge or other hardware
> implementations. On the other hand, I understand your constraints and I
> don't want to create a situation where user space is unable to
> understand how the data path works from the bridge FDB dump with
> mv88e6xxx.
>
> My suggestion is to have mv88e6xxx report the "locked" entry to the
> bridge driver with additional flags that describe its behavior in terms
> of roaming, ageing and forwarding.
>
> In terms of roaming, since in mv88e6xxx the entry can't roam you should
> report the entry with the "sticky" flag.

As I am not familiar with roaming in this context, I need to know how 
the SW bridge should behave in this case. In this I am assuming that 
roaming is regarding unauthorized entries.
In this case, is the roaming only between locked ports or does the 
roaming include that the entry can move to a unlocked port, resulting in 
the locked flag getting removed?

> In terms of ageing, since
> mv88e6xxx is the one doing the ageing and not the bridge driver, report
> the entry with the "extern_learn" flag.

Just for the record, I see that entries coming from the driver to the 
bridge will always have the "extern learn" flag set as can be seen from 
the SWITCHDEV_FDB_ADD_TO_BRIDGE events handling in br_switchdev_event() 
in br.c, which I think is the correct behavior.

> In terms of forwarding, in
> mv88e6xxx the entry discards all matching packets. We can introduce a
> new FDB flag that instructs the entry to silently discard all matching
> packets. Like we have with blackhole routes and nexthops.

Any suggestions to the name of this flag?

> I believe that the above suggestion allows you to fully describe how
> these entries work in mv88e6xxx while keeping the bridge driver in sync
> with complete visibility towards user space.
>
> It also frees the pure software implementation from the constraints of
> mv88e6xxx, allowing "locked" entries to behave like any other
> dynamically learned entries modulo the fact that they cannot "unlock" a
> locked port.
>
> Yes, it does mean that user space will get a bit different behavior 
> with
> mv88e6xxx compared to a pure software solution, but a) It's only the
> corner cases that act a bit differently. As a whole, the feature works
> largely the same. b) User space has complete visibility to understand
> the behavior of the offloaded data path.

> > I will change it in iproute2 to:
> > bridge link set dev DEV mab on|off
>
> And s/BR_PORT_MACAUTH/BR_PORT_MAB/ ?

Sure, I will do that. :-)